Spy planes able to photograph sunbathers in their back gardens are being deployed by Google and Apple.

The U.S. technology giants are racing to produce aerial maps so detailed they can show up objects just four inches wide.

But campaigners say the technology is a sinister development that brings the surveillance society a step closer.

Google admits it has already sent planes over cities while Apple has acquired a firm using spy-in-the-sky technology that has been tested on at least 20 locations, including London.

Apple’s military-grade cameras are understood to be so powerful they could potentially see into homes through skylights and windows. The technology is similar to that used by intelligence agencies in identifying terrorist targets in Afghanistan.

Google will use its spy planes to help create 3D maps with much more detail than its satellite-derived Google Earth images.